Government regulations require automobile manufacturers to control the exhaust of engine combustion byproducts such as hydrocarbons, carbon monoxide, and nitrous oxide. Emission of such byproducts is typically controlled by a catalytic converter. However, if an automobile engine misfires, an increased amount of unburned combustion byproducts is passed through the catalytic converter. Engine misfire occurs as a result of the absence of spark in a cylinder, poor fuel metering, poor compression, or other similar conditions. Over time, regular engine misfire can lead to damage of the catalytic converter.
A difficulty in the development of an on-board real-time misfire detector is the determination of a unified algorithm to detect misfires with high detection accuracy and with no false alarms while maintaining a low implementation cost, under all required engine operating conditions and misfire patterns. These operating conditions include, but are not limited to, varying engine speeds, engine loads, road surfaces, gear positions, and mechanical dynamics. Furthermore, misfire patterns may be regular, random, or special sequences.